DivinDriver

iTrader: (15)

My SA 5-speed trans, which I bought used back in the 90's, came to me without having the Overdrive Switch used on pretty much all NoAm SA RX-7's. I was told at the time I bought it, through an engine/trans importer in LA, that this was due to it being what's now called JDM. Whether or not that's true, I have no idea, but it for-certain is an SA smoothcase trans (due to shifter position), it's a 5-speed, but it has never had an overdrive switch, or even a hole for one. I've always in the past just kept the connection for it jumpered, and as far as I knew it wasn't causing me any trouble.

Now, I'm not so sure.

Recent research I've been doing on emissions control systems for the 79-80 shows that both the 4th (top gear) and 5th (overdrive) switches have a lot of control over both the entrichment system and the secondary air system, which in turn control Thermal Reactor temperature & exhaust temps.

It looks like not having a 5th gear switch might be causing the TR and the exhaust to run both too hot, and too lean, when accelerating in 5th gear below 3000 rpm, which you do a lot of on the freeways around here. This in turn may be behind the failures I've been seeing in my stock exhaust system, which always seem to result from overheat of the downpipe's first section.

So, long story short, I'm thinking I really should have that overdrive switch in place if I'm going to run stock emissions. Which means either finding a replacement SA trans (or tailhousing), or retrofitting mine, which would involve drilling/tapping the right sized hole and buying and installing a switch.

I know roughly where it installs; it's the rear-most switch on the trans, top left side, and it faces the rear. It installs parallel to the shafts in a recessed groove along the side of the trans.

If anyone has access to an uninstalled SA 5-speed, and can take a photograph and precise measurements of the hole and it's position, I'd be really, really grateful!

Or of course if they have a tailhousing and switch they care to part with...

rwatson5651

iTrader: (5)

I can help you with this. I happended across a transmission with the switches and used them to disable my radiator fan. Recently I built a "hybrid" SA trans with the gearset from a 1980 626. This meant I had to install switches in the trans case just like you are doing. I will take pics and post them asap.

t_g_farrell

iTrader: (1)

Yep, jumpering that 5th speed switch will cause you some issues with the stock
emssions setup. The ECU detects 4th and 5th gear engagement and has some
logic in place for when it sees that. I'm not surprised its causing you some
heartburn.

I'm with Robert, I use the 4 & 5 speed switches to turn off my electric fan, works
like a charm.

DivinDriver

iTrader: (15)

Thanks, gents; I look forward to getting any info available. Much as I detest having to pull the trans out (having just installed the motor) I suspect that this missing switch has cost me a lot of money and time over the years.

The more I dig into it, the more I find that gets controlled or influenced by those two switches. I'm working up a truth table by combining info from about four different 'official' sources. Will post when complete.

rwatson5651

iTrader: (5)

Here are some pics.

switch installed:


Switch pulled:


Switch:


W/ruler:


Let me know if you need other shots or measurements.

rwatson5651

iTrader: (5)

If I am not mistaken, the 4th gear switch is the same as the backup light switch. (Normally open) I think the 5th gear switch is unique. (Normally closed ?).

The thread pitch is 1.75, I remember I had a hard time finding a tap, finally found it @ McMaster Carr. I think the diameter is 12mm. I am searching for the tap to confirm diameter.

rwatson5651

iTrader: (5)

When I added my switch one issue was the case lacked the machined boss where the washer on the switch would seal. This made the case somewhat thicker and kept the switch from going deep enough. I compensated by using a thinner washer.

DivinDriver

iTrader: (15)

This is exactly the type of info I was hoping, thanks!

Info on the tap would be invaluable, as would a measurement of the 'depth' of the boss machining.

Also, if possible a shot from exactly the same straight-on angle as your final pic, but with the scale of the ruler adjacent to the casing & level with the boss but not covering anything would give me an image I can sketch, scale, and easily get an exact center from.

According the the wiring diagrams, both the Top switch and Overdrive switch are Normally Closed, which would make sense as they are wired in series. If either is activated, the circuit opens, which give it a logical "or" function; "if in either 4th OR 5th gear, circuit opens."

Funny thing is, my parts fiche doesn't show the overdrive switch. The reverse and top switch are pictured in section 1720AA, but not the overdrive switch. What SHOULD be it in the drawing based on location and shape is called out as being the reverse switch. Finding a part number might be interesting!

j9fd3s

iTrader: (3)

indeed! i put on my Mazda parts manager hat (or crack pipe, it helps if you take the same drugs as they do...) and i think i have it fingered out.

they have 17-630 as a switch, which is 1391-17-640

and then for 17-640 they have switch back up lamp, which is also 1391-17-640 and 0376-17-640A.

the 0376-17-640 says 80 model as does the 17-640 switch.

typing both into the mazda computer reveals that they are both still available, with plenty in the country

1391-17-640A is a switch, for a list of $37.09
and 0376-17-640A switch back up lamp also for $26.11

i interpret it like this. a 79 Rx7 should only have 1 switch, 1391-17-640. the 1980 model should have TWO switches 1391-17-640 AND 0376-17-640A.

looking up the tailshaft housing (17-330) give a different answer, but since the current parts availability says switch and back up light switch, i think i'd go with that. the tail housings are both NLA, so no luck there

and looking up the complete transmission reveals that the US all got the same one, 8868-03-000, vs canada with 8485-03-000, so maybe the US did ALL get both switches...

DivinDriver

iTrader: (15)

Would it throw a monkey into your reasoning (hmmm, a hairy reasoner...) if I pointed out that 79 and 80 five-speeds all had THREE switches...? The 4-speeds for both years only had two.

(The third one's not on the tailshaft. It's on the bearing carrier up front, and should be the top gear switch.)

The puzzler being, the 'third' switch physically resembles the back up switch (rubber boot with pigtail wires coming out), except that it's NC.

I wish there was some way to clarify which Mazda part number looks like the right one physically, since the overdrive switch is physcially very different both in shape and in connectors - no boot, long body, no pigtails.

Without, you know, actually having to order both.

It's good to know that they are at least still available. Provided I can figure out which one to buy!

Jeff20B

iTrader: (13)

I installed an SA 5 speed in the GLC. I recall it seemed to have two switches, which I had to make talk to the reverse light wires in the car. Not that this helps, but tells me it's from a 1980. Cool!

cfamilyfix

iTrader: (15)

Thanks Jeff....I think you just helped me wire my reverse lights with my 4 speed

Jeff20B

iTrader: (13)

Cool! And I have a spare 4 speed if the 5 ever eats its own bearings. Worldn't be the first time an SA tranny crapped out on me.

j9fd3s

iTrader: (3)

see! ok how about this. it lists 3 switches, maybe because you need all three? you use a pair of 1391-17-640's and a single 0370-17-640A?

ah ha! the 4 speed gets 1391-17-640 for the back up switch AND the commutateur switch

so that leaves 0370-17-640A as the overtop?

if it comes down to it, i've got a good relationship with my local dealer, and they would let me order both just too see which one was right.

rwatson5651

iTrader: (5)

My understanding is that the back up switch and the top switch (4th gear) are the same and the overdrive switch (tail housing) is the different one.

Both the back up switch and the 4th gear switch close when the plunger is pushed in. I have both and they appear to me to be the same switch.

The fourth gear switch is closed when in all other gears, when 4th is selected a relief in the shift fork aligns with the plunger and opens the switch. (Maybe this is why the diagram says N/C)

DD I have a good pic for you but my computer here at work will not let me access my pics @ photo bucket, if you are in a hurry pm me your e-mail address and I can send it to you from my phone, other wise I will post it tonight.

DivinDriver

iTrader: (15)

THAT explains a lot... the circuit shows as NC on the diagram but in this case the 'operational normal' is with the plunger depressed - - the opposite of the 'mechanical normal' of an uninstalled switch.

Tonight's fine, sir - -this is not going to be a quick thing, as I am currently carless during the day. The Z's at the body shop, having gotten rear-ended in North Hollywood (no jokes, now) and the -7's mechanically fine but not road legal due to not having been smogged and registered. So chasing parts isn't going to happen for a bit yet.

Especially as I'm still whingeing about having to pull it all apart again. I wonder if it's worth it / practical to try to pull just the tail housing off the trans without removing the whole thing...? probably not; I think the tunnel gets too narrow to reach every bolt and clear the shift tower. Dammit, I hate removing (actually, installing) a trans from below, but the only alternative is to pull the whole power plant and waste a ton of finished work, as well as $50 or so worth of brand-new fluids. Grrrrr.....

At least the missing switch won't interfere with the smog passage - they don't get into overdrive on the dyno test, & 4th is still sensed fine. It's passed multiple times since I swapped the trans; this is just a durability issue.

Looks to me like the 0370 is the culprit, too. Esp. in light of Dr Watson's info. Gracias.


I still wonder how I ended up with a 5-speed trans without this switch. Not sure I'm buying the "JDM" explanation I got when I bought it, as if anything Japan's smog regs in the late 70's/early 80's were more stringent than the US ones. Tokyo's smog was so bad at the time that traffic cops had to carry oxygen.

rwatson5651

iTrader: (5)

I have bought several junkyard transmissions, some have only the back up switch, others have the two additional switches, have never encountered one that had the second without the third. I have seen reference to the extra switches labeled as "California emissions". So I figured that both made their way to the US.

j9fd3s

iTrader: (3)

i think you can get the tailhousing OFF in the car, but back ON is very doubtful. if you were in the creative frame of mind you could do the 5th gear switch the german way and put it on the gear lever somehow, it doesn't have to be a big clunky switch either (i think?)

it might be canadian? Japanese emissions regulations are different from ours, i don't know details but i think the US smog laws emphasize the warm up portion more than Japans.

out warranty is longer too.

my only reference point is that the FC/FD/JC engines will pass out the tailpipe weather US or Japan spec but we get an additional warm up cat, and a warm up system (AWS)

DivinDriver

iTrader: (15)

I think the transmissions from Canuckistan have only the back-up switch.

rwatson5651

iTrader: (5)

I bought my '79 new, 4 speed car, and it came with only the back up switch.

rwatson5651

iTrader: (5)

Will this work?

rwatson5651

iTrader: (5)

I finally found the tap. It is a 12mm X 1.75. The meachined depth of the boss is very difficult to measure accurately but is approximately .085 in.

PreviouslyPlastic

iTrader: (1)

I can confirm this.
I just rebuilt the trans in mine; 1980 rx7 5 speed, only reverse light switch, but I have 2 additional wires dangling from the same loom... *shrugs*

t_g_farrell

iTrader: (1)

Probably because Canadian emissions specs were less stringent than overall US specs.

Those extra switches signalled something in the ECU to adjust the fuel delivery or burn to pass
some part of the smog specs in the US I suspect.

DivinDriver

iTrader: (15)

They actually impact a number of systems related to emissions, including the Richer circuit and the Vacuum Power Valves. They combine with the signal from the Vacuum Switch (which is an acceleration sensor, bolted to the firewall to the right of the brake booster) to control richness of mix primarily to keep the Thermal Reactor in the sweet spot between (A) hot enough to work, and (B) hot enough damage itself & the exhaust parts behind it.

TG, those pics are the bomb. Thanks so much.

I'm going to see if I can find a good and correct trans available for reasonable sale, and hold on to modding mine as a last resort. I'll be putting up a WTB in the next couple days. Got a possible line on one Middle California that I'm waiting for info on.

I guess than means I'll have another bellhousing to polish... (sigh)